Two-cycle internal-combustion engine



Nov. 5, 1929.

Fig.1.-

/ all/l/l/lll/l /////7/ C. G. CURT|$ TWO-CYCLE INTERNAL COMBUSTION ENGINE Filed March 26, 1927 :r Es

\ iv Inventor,

Charles G. Curtis Attnrney CHARLES @UZPJEKS, OF NEW Edit-HQ, Y.

TJVQ-CYCLE INTERIEQAL-GQMEUSTION ENGINE .lpplication filed March 26,

- This invention relates to and has as its object the improving oi the scavenging efiiciency of two-cycle engines of the portscavenged type.

it has been common practice in portscavenged engines, particularly in the small sizes, to build the cylinders with radial inlet air ports (that is ports pointing towards the center of the cylinder) and to use protruding flanges or battles on the piston heads which deflect the streams of incoming scavenging air towards the combustion end of the cylinder. Such engines have generally hada low scavenging eiiiciency, so that they have had to be operated at comparatively low mean effective pressures in order to avoid smoke and to give'a reasonable fuel efficiency. They have also been open to the objection that the battles or flanges are liable to heat strains which cause cracking or a wearing away, and they have not been used commerciallyto any considerable extent except in small engines.

Recognizing the possibility of materially improving the scavenging efi'iciency of such engines (that is engines with radial ports, either horizontal or inclined) I have carried 7 on elaborate experiments to determine the conditions under which the best efficiency can be obtained and I have discovered that there is a relationship between the height of the battle head and the height of the ports and between the shape and width or area of the gap between the bafile and the adjacent cylinder wall and the area of the inlet ports, which relationship has a verymarked influence on the scavenging efliciency.

The prior art is full of incidental disclosures of both horizontal and inclined radial inlet ports directing the air streams against protruding bailles on the piston head, but I do not find any disclosure of the relationship necessary for high scavenging efiiciency.

On the accompanying sheet of drawings which forms a part of this description,

Figure 1 of the drawing is a sectional elevation of an engine cylinder showing the ports and piston head with bafile on the line II of Fig. 2. s

Fig. 2 is a section on the line II-II of 3.5327. Serial No. 178,616.

Fig. 1 showing the gap between the bafiie and the cyl nder. wall.

In F 1g. 1 a cylinder 3 has air inlet ports a, a piston 5 with a bathe 6, and exhaust ports 7. Assuming that the air inlet ports extend about half way around the circumference the baiiie should be carried around so as to a little more than cover these inlet ports leaving an annular space or gap between the battle and the cylinder wall through which the air flows in a generally upward direction. In order to produce a high scavenging efficiency it is important that the column or streams of air be made to shoot upward at sutficientlv high Velocity and along the surface of the cylinder wall so as to pass up to the combustion end on one side of the cylinder and interfere as little as possible with the downward movement of the column of air on the other side of the cylinder and out through the exhaust ports.

The area of the gap between the baflie and the adjacent cylinder wall plays, I have found from experiment, a very important part in the scavenging efliciency. It should be made small enough so that a part of the total pressure drop from the scavenging air supply pressure to the cylinder pressure takes place at this point whereby a velocity is set up in the desired direction, that is toward the cylinder cover and as nearly parallel to the cylidncr wall as practicable. If this area be made less or no more than the total area of the ports a considerable velocity is set up due to the drop in pressure at this point. In other words by contracting this area a nozzle throat condition is established and the greater part of the total pressure drop takes place here instead of in the ports themselves. This insures a better directed scavenging air stream with sufficient velocity to carry to the cylinder cover. Even if the area of the gap and that of the ports are made equal a substantial part of the total pressure drop will take place at the gap.

The area of the ports is of course determined not only by the height of the ports but by the thickness of the bridges between the several ports. For practical reasons these bridges should not be made too thin and should probably be made equal to at least one 2 risen third of the pitch of the ports. The ports would then occupy about two thirtis or" the total are covered by the bank of ports. The area of the gap should be adjusted with reference to the efi'ective or combined area of the ports. If the area of the gap materially exceeds the area of the ports the scavenging ethciency fails ofi very rapidly and e inateriai increase in the amount of scavenging air is necessary unless an objectionable b'afie height is resorted to.

I have also found by my experiments that the height of the bafie relative to the height of the port is an important factor in produo mg high scavenging eficiency. it is important that the height of the bafie shouhi in any event be not iess than the height of the port. A still better scavenging eficiency can be ob tained by carrying the bafie to a height more or iess above that of the port preferably as much as ten percent higher than that of the port, but for practical reasons on account of heat strains, danger of cracking and the difficuity of forming a goori combustion space, it is very desirable to keep the height of the batfie as low as possible. By combining a gap area no greater or iess than the totai port area with a baihe height which is substantiaiiy as high as or higher than the port height, am able to secure much higher scavenging efficiencies than heretofore. The result is that twocycie engines of this type can now be operated at consiclerabiy higher mean efiective pressures and at higher fuel efiiciencies without necessitating the use ozt any greaterernount of scavengingair or of using scavenging air at any higher pressures than heretofore.

The cycle of operations is the same as is common to sit simple ports scavenger]. twocycie engines anti hence need not be described here.

What I claim is:

' 1. A port-sca engeoi tWo-cycie engine comprising a cylinder, air inlet ports on one side of the cylinder, exhaust ports on the side opposite, a piston and a bafile on the piston head so arranged and proportioned that the area of the gap betweenthe bafie and; the cylinder Wait is no more than the totai' area of the air inlet ports.

A port-scavenged two-cycle engine comprising a cylinder, air inlet ports on one side of the cylinder, exhaust ports on the siiie opposite, a piston and a bafie on the piston head so arranged; and proportioned that the r area of the gap between the bafie and the cylinder Wall is no more than the total area oi the air inlet ports and the bafie is at least as high as the air iniet ports.

Ci-EARLES G. UURTKS. 

